Angular Leaf Spot - Time to Worry?

May 6, 2024

Following the rain of this past week Saturday, we've been hearing about a pretty significant outbreak of angular leaf spot in strawberry.  We include some pictures from a field of Cabrillo taken the morning of May 6.

In the way of review, angular leaf spot in strawberry is caused by the bacterial pathogen Xanthomonas fragariae, and manifests itself as you can see in all the photos below. In particular, the underside of the leaf will take on a watery appearance in vein delimited areas of the leaf (Photo 3), and in often in the morning have a sort of goo there (and it is real sticky, brush your finger over it and you will know, this is the cytoplasm from the lysed plant cells).

Addressing the question: Is this a time to worry?  All things considered, we think probably not, unless it rains again.  What is very likely the cause of this heavier than average outbreak of angular leaf spot this year is the greater frequency of rainstorms, in other words unlike last year with huge intense rains interspersed with longer periods of dry, this year has experienced lighter rains but at more frequent intervals, creating lengthier durations of free moisture on the leaves which has created good growth conditions for Xanthomonas fragariae.  

So if the trend from here on out is dry as it is supposed to be, there is less reason to worry about this outbreak becoming worse and causing trouble.